The Spinal Cord
Basic Neuroscience
James H. Baños, Ph.D.
Grey and White
Matter
Grey and White Matter
Grey Matter = Cell Body
White Matter = Myelinated axon
Grey and White Matter
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Grey matter
Cortex
 Nucleus (CNS)
 Ganglion (PNS) Exception: Basal Ganglia
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Grey and White Matter
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White Matter
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Nerve (PNS)
Tract (CNS)
Fasciculus/Funiculus -- Group of fibers with common origin and
destination
Lemniscus -- Ribbon-like fiber tract
Peduncle -- Massive group of fibers -- usually several tracts
Grey and White Matter

Tracts are named with origin first, then
destination
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Corticospinal tract -- cortex to spinal cord
Mammilothalamic tract -- Mammilary bodies to
thalamus
Spinocerebellar tract -- Spinal cord to cerebellum
Corticobulbar tract -- Cortex to brain stem
The Spinal Cord
General Organization

Spinal cord is SMALL!
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42-45 cm long
1 CM wide at widest point
Does not extend all the way to the bottom of the spinal column
Pattern of grey/white matter is reversed in the cord
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White matter tracts on outside
Grey matter on the inside
Staining reverses this!!!
General Organization
White matter (tracts
of axons)
Grey Matter
(cell bodies)
General Organization

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Spinal cord is segmented anatomically
Input and output occurs in groups of rootlets
arranged in a series longitudinally along the cord
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Dorsal rootlets -- Input -- carry sensory information
Ventral rootlets -- Output -- motor neurons
General Organization
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Each set of rootlets forms a spinal nerve
that innervates a corresponding segment
of the body, called a dermatome
General Organization
General Organization

There are 31 segments in the spinal cord:
8 cervical (C1 - C8)
 12 Thoracic (T1 - T12)
 5 Lumbar (L1 - L5)
 5 Sacral (S1 - S5)
 1 Coccygeal

General Organization

The spinal cord is housed within the
vertebral column
General Organization

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Each cord segment has a
corresponding vertebra of
the same name (e.g., C3)
Spinal nerves enter/exit
underneath their
corresponding vertebral
segment
General Organization

But wait! Something doesn’t add up!
How can spinal nerves exit below their
corresponding vertebral segment if the cord is
only 42cm-45cm long?
 Answer: Spinal nerves extend down to the
appropriate vertebral segment forming the
cauda equina

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This means cord segments and vertebral
segments don’t line up
General Organization
General Organization

Cord is not of uniform thickness
throughout its length. Why not?
General Organization

Cord is not of uniform thickness
throughout its length. Why not?

Answer:
Segments of the cord innervate parts of the
body that differ in complexity
 There are fewer white matter tracts lower in
the cord.

General Organization
Cervical enlargement
C5 - T1
Lumbar enlargement
L2 - S3
The Spinal Cord in
Cross Section
Cord Sections
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Segments of the spinal cord have a similar
organization, but vary in appearance.
Always know where you are in the cord
(i.e., cervical, thoracic, lumbar, sacral)
Cord Sections -- Cervical
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Cervical cord is wide,
flat, almost oval in
appearance. Why?
Cord Sections -- Cervical Enlargement

What’s different about
the cervical
enlargement . Why?
Cervical
Cervical Enlargement
Cord Section -- Thoracic
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Less White matter
than cervical
Rounder appearance
Less prominent
ventral horns than
cervical enlargement
Cord Section -- Lumbar
Lumbar
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Lumbar Enlargement
Less White matter
than thoracic
Rounder appearance
Larger ventral horns,
especially in lumbar
enlargement
Cord Section -- Sacral
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Not much white
matter
Mostly grey, although
not much of that
either
Cross Sectional Organization
Posterior intermediate sulcus
Posterior median sulcus
Tract of
Lissauer
Anterior white commisure
Anterior median fissure
Grey Matter
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Laminar
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Laminae of
Rexed
Grey Matter
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Posterior (dorsal)
Horn
Intermediate Grey
Anterior (ventral)
Horn
Grey Matter: Posterior Horn

Mostly Interneurons
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Substantia gelatinosa
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Pain/temp proc
Body of the posterior
horn
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Sensory proc
Grey Matter: Intermediate Grey
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Clarke’s Column
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T1-L3
Balance/proprio.
Intermediolateral
Column
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T1-L3
Sympathetic neurons
Grey Matter: Anterior Horn
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Lower Motor
Neurons
White Matter: The “Big Four” Pathways
Corticospinal tract
Dorsal Columns
Spinothalamic tract
Spinocerebellar tracts
The Big Four
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Corticospinal tract
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Dorsal columns/ medial lemniscus
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Discriminative touch
Conscious proprioception
Spinocerebellar tract (dorsal and ventral)
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Voluntary motor
Unconscious proprioception
Spinothalamic tract
 Pain/temperature
Corticospinal Tract
Voluntary Motor
Corticospinal Tract
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First order neuron (upper motor neuron) originates in
precentral gyrus
Passes through internal capsule
90% decussates in caudal medulla
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10% undecussated
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Lateral corticospinal tract
Anterior corticospinal tract
Synapses on second order neuron (lower motor neuron)
in ventral gray of the cord
Second order neuron innervates muscle
Motor Homunculus
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
HAL
Motor Homonculus
HAL:
Arms
Head
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Legs
QuickTime™ and a
Microsoft Video 1 decompressor
are needed to see this picture.
Corticospinal Tract
Spinal Cord
Medulla
Pons
Midbrain
Upper & Lower Motor Neurons
Motor Ctx
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Upper Motor Neuron
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UMN
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Lower Motor Neuron
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Ventral
Grey Horn
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Ventral Grey Horn to Neuromuscular Junction
Efferent of stretch reflex arc
Helps maintain tone
Sensory Neuron
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LMN
Motor Cortex to Ventral Grey Horn
Modulatory influence on stretch reflex arc
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Stretch receptors in muscle and tendons
Helps maintain tone
Afferent of basic stretch reflex arc
Upper & Lower Motor Neurons
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UMN
LMN
Maintenance of Tone
 Input from stretch receptors causes
lower motor neuron to supply tonic
stimulation to the muscle
 The upper motor neuron modulates
this -- will tend to “override” the
tonic signal from the sensory
neuron
Upper & Lower Motor Neurons
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UMN
LMN
Reflex Arc
 Afferent is sensory neuron
detecting a sudden stretch
 Signal is strong and results in a
strong response by the lower motor
neuron
 Strong signal usually overcomes
mild cortical input from the UMN
Upper & Lower Motor Neurons
Motor Ctx
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Upper Motor Neuron Signs
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UMN
Ventral
Grey Horn
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Why?
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LMN
Spastic paresis
Hypertonia
Hyperreflexia
No muscle atrophy (until perhaps late in the
course)
Positive Babinski
Loss of voluntary UMN signal
Loss of modulation of tone and reflexes by
UMN -- the circuit runs unchecked
Upper & Lower Motor Neurons
Motor Ctx
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Lower Motor Neuron Signs
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UMN
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Ventral
Grey Horn
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Why?
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LMN
Flaccid paresis/paralysis
Muscle fasciculations
Hypotonia
Hyporeflexia
Muscle atrophy
Negative Babinski
Loss of LMN for voluntary movement
Loss of efferent component of reflex arc and
tone pathway
Babinski’s Sign

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In response to stimulation of the sole of the foot,
the toes will usually curl downward.
When UMN inhibition is removed, the toes will
curl upward (Dorsiflexion). This is referred to as
a positive Babinski or presence of Babinski’s
sign.
Related Terms…

Spasticity -- Increased muscle tone and
increased reflex contraction (UMN)

Clonus -- Rythmic contractions and
relaxations seen when a spastic muscle is
stretched (UMN)
Basics of Localization
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If all limbs are checked for upper and
lower motor neuron signs, you can begin
to localize lesions
Left-right differences are also very
important
Dorsal Column/
Medial Lemniscus
Discriminative Touch
Conscious Proprioception
Dorsal Columns/Medial Lemniscus
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First order neuron begins in receptor
Enters cord at tract of Lissauer
Legs run in fasciculus gracilis (medial dorsal)
Arms run in fasciculus cuneatus (lateral dorsal)
Synapse on nucleus gracilis and nucleus cuneatus
(caudal medulla)
2nd order neuron decussates and runs from NG & NC to
thalamus (as medial lemniscus)
3rd order neuron runs from thalamus to postcentral
gyrus
Dorsal Columns/Medial Lemniscus
Spinal Cord
Medulla
Pons
Midbrain
Spinocerebellar Tracts
Unconscious Proprioception
Dorsal (Posterior) Spinocerebellar Tract
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Involves Clark’s Column, a longitudinal gray matter body
from about T1 to L3
Below Clark’s Column:
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Level of Clark’s Column
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Runs with f. cuneatus, synapses in Clark’s Column, joins dorsal
spinocerebellar tract
Synapses in Clark’s Column, joins dorsal spinocerebellar tract
Above Clark’s Column
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Runs with f. cuneatus, synapses in lateral cuneate nucleus
(caudal medulla), projects to ipsilateral cerebellum
Dorsal (Posterior) Spinocerebellar Tract
L3
Spinal Cord
T1
Medulla
Pons
To Cerebellum
Midbrain
Ventral (Anterior) Spinocerebellar Tract
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Supplements Dorsal Spinocerebellar Tract
Information from more diverse array or receptors
Originates from scattered cells in the
intermediate grey caudal to L1 (which in turn
have input from proprioceptive axons or their
collaterals
Crosses twice, to end up in ipsilateral
cerebellum
Ventral (Anterior) Spinocerebellar Tract
Spinal Cord
Medulla
Pons
Midbrain
Spinothalamic Tract
Pain and Temperature
Spinothalamic Tract
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First order neurons originate in pain receptors, enter
cord at tract of Lissauer, and synapse in substantia
gelatinosa or nucleus proprius
Second order neurons cross at the anterior white
commissure, rising 1 or 2 cord levels in the process, and
form contralateral spinothalamic tract
A third order neuron (not technically spinothalamic tract)
projects to the cortex
Spinothalamic Tract
Spinothalamic Tract
Spinal Cord
Medulla
Pons
Midbrain
L1
L1
L2
L2
L3
L3
L4
L4
L5
L5
Coming Up…
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Lab Week Overview: Monday
Virtual Labs
Wet lab day: Thursday
Lab Practical Exam: Friday